Light-emitting diodes intended for indication purposes have been used for a long time, but high-brightness LEDs, e.g. LEDs having a brightness that is high enough to enable general illumination of various locations such as rooms, have in a short period of time caused a significant growth in the LED and lighting applications market. High-brightness LEDs are generally associated with a small size, a relatively high efficacy (and associated low temperature), a relatively long lifetime, a wide color gamut and ease of control. Naturally, such LEDs are of importance to lighting designers in developing new lighting applications. Such LEDs may also be utilized in replacing conventional light generation devices, such as filamented light bulbs or halogen lamps. Such LEDs are also generally capable of emitting light of various colors. Thus, as the performance of LEDs improves and the costs of LEDs decreases, LEDs are expected to a significant degree replace conventional light sources such as incandescent lamps and fluorescent tubes. Furthermore, LEDs are in general compact compared to such conventional light sources.
For example, LEDs may be of such small size as to enable arrays of LEDs to be arranged on the surface of clothes, handbags, backpacks, furniture covering, carpets, window shades, curtains, etc.
To efficiently realize unobtrusive lighting solutions using such LEDs, not only are light sources having a relatively small size needed but also means for transporting light from the light source and distribute the light over a surface or throughout a volume. Light guides are known for spreading and transporting light. In general, light from a LED is injected into one side of the light guide and emerges from another side of the light guide by means of light extraction means. In order to inject light from a LED into a thin light guide, such as a thin optical fiber or a thin plastic sheet, the beam of light from the LED generally has to shaped appropriately, as a typical light-emitting area of a LED is about 1×1 mm2, while a typical diameter of an optical fiber is about 100 μm and a typical thickness of a thin plastic sheet used as a light guide may be about 200 μm.
In particular in the field of beam shaping, new options of so-called secondary optics such as lenses and/or mirrors have become available where optical elements are positioned close to the LED for converting the emission pattern of the LED, which often is Lambertian, into another, desired pattern, such as a narrow cone-shape pattern. In general, such secondary optics are constituted by combinations of one or more LEDs and a separate optical beam-shaping element. Thus, two or more components in general have to be positioned in a desired position relatively each other in order to achieve the desired beam-shaping and be maintained in the desired position, accurately and securely. Such solutions may hence pose mechanical difficulties with regards to assembly and/or use.
In general, available secondary optics is relatively large, especially in comparison with the light-emitting area of a LED. A typical diameter of secondary optics may range from about 20 mm to about 50 mm, and the thickness of secondary optics may typically range from about 10 mm to about 20 mm, to be compared with the light-emitting area of a LED that is typically about 1×1 mm2. Thus, such secondary optics are in general relatively bulky and/or obtrusive.